Post by c***@physics.ucdavis.eduPost by Blaze LabsHello guys,
I would like to know the main reasons why the push gravity concept is
not considered as a viable concept by mainstream science.
There are a few generic objections, along with particular problems with
particular models. The main generic objections I know of are
1. Drag: As Feynman pointed out in the Feynman Lectures, anything
that's capable of "pushing" will also create drag on a moving object.
There are very strong observational limits on such drag, in the
Solar System and in binary pulsar systems.
I assume (perhaps incorrectly) that you are referring to the paragraph
in Vol. I, pages 7-9 to 7-10, in which Feynman commented on the theory
of a mechanism of gravitation. I was thinking that if these
"push-particles" are traveling at the speed of light, c, something like
the following might hold. Let F be the flux of these particles thoughout
space (i.e., the number of particles passing through unit area in unit
time.) Also, assume the flux is isotropic in direction. Consider a thin
sheet of matter traveling at speed u in the +X direction (traveling
broadside so you see the full area when looking along X.) To simplify,
consider only those particles going either in the +X or -X direction.
(Nothing is lost, in principle, by doing this, as you could integrate
over velocity components for other directions.) When the object is at
rest, it sees the same particle flux, F,coming from both the front side
and the hind side. But in motion, the flux it meets is increased to
F(c+u)/c and the flux from behind is decreased to F(c-u)/c. If Feynman's
anology with running in the rain applies, the thing would certainly
absorb more particles from the front than from the back per unit time,
and would feel a resistance to the motion. (With raindrops, if they hit,
they are absorbed.) However, the sheet of matter is composed of
individual absorber particles, say "atoms". Looking at a single atom,
the number of encounters per second it has with a push-particle is
proportional to the particle flux in the vicinity of the atom. The
number absorbed per second by that atom is equal to the number of
encounters per second times the probability, p, of absorption per
encounter.So, for push-particles coming from the front, an atom in the
sheet of material would absorb
N(1) = ApF(c+u)/c particles per second (1)
where A is the proportionality constant mentioned above for encounters,
and p is the probability of absorption per encounter.
This same atom would absorb from behind,
N(2) = ApF(c-u)/c particles per second. (2)
If the probability were the same in each case, the atom would certainly
absorb more per second from the front than from behind. However, the
atom (or whatever absorbing "particle") may be assumed to have an
effective absorbing diameter,d. A particle can be absorbed by it only
when it is traversing this distance through, or close by, the atom. It
takes a time t(1) = d/(c+u) for the particles meeting the atom to
traverse its sphere of influence. And for those coming from the rear, it
takes a time t(2) = d/(c-u) for them to get away from its influence. The
probability of absorption per encounter should also be proportional to
the time lapse of the encounter. (if it stays in the vicinity of the
atom longer, it should have a higher probability of absorption.)
Therefore, the probability of absorption in each case would be p(1) =
Bd/(c+u) for particles meeting it, and p(2) = Bd/(c-u) for particles
coming from behind, where B is the proportionality constant.
Replacing the probability p in equations (1) and (2) above with these
probabilities as a function of the time lapse of encounter, gives:
the number absorbed from the front per second by a given atom as
N(1) = A[Bd/(c+u)]F[(c+u)/c] = (ABdF)/c
and the number absorbed from behind per second by the same atom
as:
N(2) = A[Bd/(c-u)]F[(c-u)/c] = (ABdF)/c
The result is the same, which shows that a moving object will absorb the
same number per second of push-particles from the front as from the
back. Therefore the object will feel no net force due to motion in this
isotropic flux of particles. (If one worries about the energy build-up,
we may assume that the particles, once absorbed, are very quickly
re-scattered isotropically.)
Whether I'm right or not,
Have one on me!
Post by c***@physics.ucdavis.edu2. Aberration: Suppose "pushing" particles move at a speed v, and
look at the effect on the Solar System. For a planet at distance d
from the Sun, the "push" will not be toward the instantaneous
position of the Sun, but towards its position at a time d/v in the
past. This is a drastic effect -- if v is the speed of light, the
Solar System would be drastically unstable over a thousand-year
time scale.
(The effect of aberration is to increase the velocity of a planet,
and you might hope that drag would cancel it. But it's easy to
check that such cancellation can occur at, at most, one radial
distance from the Sun.)
3. Principle of equivalence: It is observed that gravity acts not
only on mass, but on all forms of energy. A "push gravity" theory
would have to come with an explanation of how the particles that do
the pushing manage to push against, for example, electrostatic binding
energy and the kinetic energy of electrons in an atom, and why that
"push" exactly matches the "push" against ordinary matter.
In particular, we observe that gravitational binding energy itself
gravitates. This seems to require self-interaction among the
pushing particles. On the other hand, the accuracy of the inverse
square law over long distances requires that the self-interaction
be very small -- you certainly need a mean free path larger than
the size of the Solar System if you don't want to mess up Pluto's
orbit.
4. Gravitational screening: There are very strong limits on the kind
of "gravitational screening" one would expect from a "push gravity"
model -- see, for example, Unnikrishnan et al., Phys. Rev. D 63 (2001)
062002.
[...]
Post by Blaze LabsPlease note, I am NOT asking about Le Sage ultramundane particles
theory (which also falls under the push gravity category), which I can
easiely discredit myself. I'm mostly interested in the concept of
electromagnetic radiation pressure of high frequency radiation acting
as the gravitational mechanism, and its shadowing creating the inverse
square law, low pressure areas.
You immediately run into trouble with the principle of equivalence,
for one thing. Electromagnetic waves don't interact with other
electromagnetic waves (except by truly tiny quantum effects); but
gravity bends light. Nor do electromagnetic waves interact with
internal energy, not with neutrinos; but these *are* affected by
gravity. You also run into grave problems with aberration (see above),
and very probably with drag. You would *further* have to explain why
this high frequency radiation is not absorbed by the Earth enough to
lead to gravitational screening of the type ruled out by experiment.
Note that "high frequency [electromagnetic] radiation" is gamma radiation.
There are experimental measurements of very high energy gamma rays, and
a fair amount is known about their spectrum. I suspect you would have
a very hard time reconciling your model with these observations.
Steve Carlip